1. Field of the Invention
The present invention relates to a method of determining a distance to be moved by an optical pick-up, where a distance from a current track to a target track is determined by an exact single track width formed on an optical disc. More specifically, the present invention relates to a method of determining a distance to be moved by an optical pick-up to achieve uniform access time for various optical discs, regardless of differences in size of the single track width formed on those optical discs.
2. Description of the Related Art
FIG. 1 shows the structure of a conventional drive/detection unit which drives the optical disc and detects signals therefrom. A pick-up 11 reads recording signals that are detected based on light which is incident on, and is reflected from, the surface of an optical disc 10. A sled motor 12a moves the pick-up 11 in a radial direction across the disc 10. A spindle motor 12b rotates the disc 10. A driver 30 drives both the sled motor 12a and the spindle motor 12b. An R/F unit 20 filters and normalizes the signals detected by the pick-up 11. A servo unit 40 receives focus error signals (FES) and tracking error signals (TES) output from the pick-up 11, and controls the rotation rate of the spindle motor being driven by the driver 30. The servo unit 40 also detects synchronization of the output signal from the R/F unit 20. A digital signal processor (DSP) 50 recovers the signal read by the R/F unit 20 into an original digital signal, using the detected synchronization. A microprocessor 60 controls the movement of the pick-up 11 and thus the play of the disc 10.
The pick-up 11 moves in a radial direction across the disc 10 during the play thereof and continuously detects the R/F signals recorded thereon. The R/F unit 20 filters and normalizes the R/F signals detected by the pick-up 11. The servo unit 40 detects synchronization of the filtered and normalized signals. The DSP 50 recovers the R/F signals output from the R/F unit 20 into original digital data, using the detected synchronization, the data ultimately being converted into moving picture data.
When a user directs the microprocessor 60 to perform a search mode (i.e., requests play of a target track located away from the track being currently read by the pick-up 11), the microprocessor 60 detects the current position information of the pick-up 11 from digital data, which is play information input from the DSP 50, and detects the number of the current track corresponding to the position information. The position information may be minute, second, and block (MSB) data in the case of CD, while it may be sector numbers in the case of DVD. The number of tracks to be crossed by the pick-up and the direction of movement of the pick-up are then determined, depending on the difference of the track numbers between the current track and the target track.
With this information known, the microprocessor 60 then calculates the distance from the current track to the target track by multiplying the number of tracks to be crossed by a standard single track width of the disc, which is known to those skilled in the art. Once the distance to be moved by the pick-up 11 is calculated, the microprocessor 60 controls the driver 30 via the servo means so that a drive current is output to the sled motor 12a. The sled motor 12a is rotated in proportion to the time of applying the drive current causing the pick-up 11 to move by an exactly calculated distance in the desired direction.
After the pick-up 11 moves the exactly calculated distance, it reads the track information at the moved position and identifies whether the track being read at the moved position is the target track requested by the user. If the track being read at the moved position is not the target track, the pick-up 11 performs a fine search mode. In the fine search mode, pick-up 11 moves to a second position which is located a small distance away from the track being read and reads the track information at the second position. This fine search mode is repeated until the target track is found.
It is well known to those skilled in the art that a standard single track width of an optical disc is generally 1.6 .mu.m. However, the real single track width formed on the disc may very depending on the manufacturing conditions or higher integrity of data thereof. That is, tracks formed on the optical disc do not have a single uniform track width. In reality, a single track width of the optical disc having a range of 1.5 to 1.7 .mu.m is acceptable, and thus the real tracks of the optical disc are formed within this range. Nonetheless, when the microprocessor 60 calculates a distance to be moved by the pick-up 11, the microprocessor 60 always identifies the single track width of the disc to be 1.6 .mu.m.
As a result, if the real single track width formed on the disc is less than 1.6 .mu.m, the pick-up 11 may overshoot the target track during a search mode. On the other hand, if the real single track width formed on the disc is more than 1.6 .mu.m, the pick-up 11 may not reach the target track during a search mode. In those cases, additional time is needed for performing a fine search mode (e.g., 150 to 200 msec.) In some cases, additional time of 2 to 3 sec is needed. This results in much longer time for accessing a desired target track.